Rammed earth, on the other hand, is considered one of the more benign ways to build, using a local material, carefully rammed into molds. But it is labor intensive. It's also not usually pure rammed earth, but is really a form of low-cement concrete with as much as 7% cement to stabilize it and keep it from washing away in the rain. (Regular concrete is 15-20% cement)

Rammed earth in a block

Watershed Block takes the best of both worlds. Developed by rammed earth builder David Easton, it is essentially pretty close to a rammed earth block that can be laid by any mason and treated like a normal concrete block. Under high pressure, the locally sourced minerals go under a process of "lithification" where the grains of sediment are converted into rock. The cement helps bind it together, making a lovely to look at block with half the CO2 footprint of conventional cement blocks. It comes in various colors and tones, depending on the source of the sediments used.

It has a lovely warm look to it, that shows off really well in these interior shots. Unfortunately, right now it is only available within 200 miles of San Francisco, but they seem to be travelling around America looking for other places to make it. They claim on their website that it only costs 15 to 20% more than conventional dyed concrete blocks, but look at all the savings on interior finishes if you just use this instead of drywall.